The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes
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Descriptions

Phytophthora infestans is a destructive plant pathogen best known
for causing the disease that triggered the Irish potato famine and
remains the most costly potato pathogen to manage worldwide.
Identification of P. infestan’s elusive center of origin is critical to
understanding the mechanisms of repeated global emergence of
this pathogen. There are two competing theories, placing the origin
in either South America or in central Mexico, both of which are
centers of diversity of Solanum host plants. To test these competing
hypotheses, we conducted detailed phylogeographic and approximate
Bayesian computation analyses, which are suitable approaches
to unraveling complex demographic histories. Our analyses used
microsatellite markers and sequences of four nuclear genes sampled
from populations in the Andes, Mexico, and elsewhere. To infer the
ancestral state, we included the closest known relatives Phytophthora
phaseoli, Phytophthora mirabilis, and Phytophthora ipomoeae,
as well as the interspecific hybrid Phytophthora andina. We
did not find support for an Andean origin of P. infestans; rather, the
sequence data suggest a Mexican origin. Our findings support the
hypothesis that populations found in the Andes are descendants
of the Mexican populations and reconcile previous findings of ancestral
variation in the Andes. Although centers of origin are well
documented as centers of evolution and diversity for numerous crop
plants, the number of plant pathogens with a known geographic
origin are limited. This work has important implications for our understanding
of the coevolution of hosts and pathogens, as well as
the harnessing of plant disease resistance to manage late blight.